A magnetic conductor corresponds to a general electric conductor. A tangential component of an electric field is almost ‘0’ on a surface of the electric conductor, while a tangential component of a magnetic field is almost ‘0’ on a surface of the magnetic conductor. Thus, different from the electric conductor, no current flows on the surface of the magnetic conductor.
The magnetic conductor operates as a component which has a considerably high resistance in a specific frequency range, i.e., performs as an open circuit due to its characteristics. Specific unit cell patterns may be periodically arrayed on the general electric conductor to realize the magnetic conductor. In this case, the magnetic conductor is referred to as an artificial magnetic conductor (AMC).
A surface of the AMC has a high impedance surface (HIS) characteristic. The HIS characteristic depends on a specific frequency according to the AMC patterns.
An antenna generally requires a distance of ¼ or more of a wavelength λ of a transmitted and received signal from a ground surface of the electric conductor. If the antenna is at a closer distance than λ/4, a surface current flowing in an opposite direction to a current flowing in the antenna is inducted to the ground surface of the electric conductor. Thus, the two currents offset each other and the antenna cannot operate well.
However, since a current does not flow on a surface of the AMC, the antenna operates much closer to the AMC than the electric conductor. As a result, a distance between the ground surface and the antenna can be reduced. A new ground according to the characteristic of such an AMC is used as a surface of an antenna of a conventional mobile communication terminal having a feeding port.
FIGS. 1A and 1B are side and perspective views of an AMC used in a conventional antenna.
Referring to FIG. 1A, an AMC 10 includes a ground layer 18, a first dielectric layer 14, an AMC layer 12, and a frequency selective surface (FSS) layer 22.
The AMC layer 12 is connected to the ground layer 18 through vias 16, and the FSS layer 22 is connected to the ground layer 26 and a power source to form a capacitor 24.
Referring to FIG. 1B, the AMC layer 12 is simply patterned in arrays of square patches. The square patches are electrically connected to the ground layer 18 through the vias 16 formed of a metal. A monopole type antenna (not shown) is mounted on the AMC layer 12, and the FSS layer 22 may be capacitively loaded in order to reduce a length of the antenna.
The first dielectric layer 14 is formed at a distance of about 1/50 of a wavelength λ of a transmitted and received signal. The conventional antenna does not require a distance of ¼ or more of a wavelength of a transmitted and received signal from a ground layer due to the AMC.
As described above, the AMC shown in FIGS. 1A and 1B includes the vias 16, and a conventional antenna such as a monopole antenna is mounted on the AMC. The monopole antenna is supplied with power from a feeding port. Accordingly, since the vias 16 have to be included in the AMC, the manufacture of the AMC is complicated. Also, since the conventional antenna includes the feeding port for supplying power, a structure of the conventional antenna is complicated, and a size of the conventional antenna is increased.